“Click chemistry” is the class of reactions that resemble natural, biochemical reactions, with the following attributes: highly efficient, “spring-loaded” reactions that proceed rapidly to high yield; highly selective reactions that produce no (or few) side products and are tolerant of multiple functional groups; and reactions that proceed under mild reaction conditions, such as at low temperatures (e.g., ambient) or in aqueous solutions.
Click chemistry has grown to encompass a range of chemical reactions, such as Diels-Alder reactions, copper-catalyzed alkene-azide cycloaddition (CuAAC), thiol-maleimide addition reactions, and thiol-alkene and thiol-alkyne addition reactions.
The term “thiol-ene” is generally used to describe the hydrothiolation addition of a thiol to any of a wide variety of unsaturated functional groups, such as maleimides, acrylates, and norbornenes, in addition to unactivated carbon-carbon double bonds. In some cases, the reaction can take place not only via the classical radical addition mechanism, but also with Michael-type nucleophilic addition. The term “thiol-yne” is used to describe counterpart hydrothiolation methods using an alkyne in place of an alkene. In general, the thiol-ene and thiol-yne reactions are conducted under photo-initiated radical conditions and proceed via a typical chain growth process with initiation, propagation, and termination steps.
The thiol-ene and -yne click reactions have many attractive features for polymer synthesis. The reactions are rapid, stereo-specific, insensitive to water, and can provide a variety of polymer functionalities through the use of various thiol and/or alkene/alkyne functionalized monomers. By using di-, tri-, and tetra-functionalized thiol and alkene/alkyne monomers, it is possible to perform thiol-ene and -yne click reactions to build new materials with a variety of chemical functionalities. These reactions may also result in more highly organized polymeric networks, in comparison to similar acrylate polymers.
There exists a need for separation or chromatography media that can be easily made by fast, efficient, and easily-controllable polymerization reactions, and easily modified. These media must also display high selectivity and high flow velocity, low back pressure, be inexpensive, and allow for long column-lifetimes, short process-times, and overall operational flexibility.